ISSUE:

Some dedicated CNG vehicles may exhibit various driveability conditions due to a loss of injector performance, resulting from fuel quality. The conditions (in approximate order of their occurrence) include:

Loss Of Power At Heavy Load

DTC Codes For Lean Fuel

Rough Idle

Hard Start

Plugged Catalytic Converter

No Start

NOTE:

THE HARD START AND NO START TYPICALLY WILL OCCUR AT THE FIRST START OF THE DAY AND DURING THE FIRST COLD DAYS OF FALL OR WINTER.

ACTION:

The root cause of these conditions may be due to either excessive or insufficient carryover compressor oil from the CNG fill station.

Excessive carryover compressor oil is oil greater than Ford’s recommended concentration levels of 10 to 80 Parts Per Million (PPM). Oil can then be carried to the injectors as a mist in the gaseous fuel stream or as a liquid film on the inner walls of the fuel rail. The liquid oil can collect inside the injector and then form a semi-solid deposit over time. The deposits do not restrict fuel flow once the injector is opened, but may delay opening or prevent an injector from opening at all. The deposit may increase over time and may further delay the injector opening time. Insufficient oil (less than 10 PPM) may lead to wear and roughening of the injector pintle, increasing the force required to open the injector, especially when cold. In either case, the customer may first notice a loss of power, rough idle, and overheated catalysts. A lean DTC code will be set when the adaptive fuel logic adjustment range for injector pulse width is exceeded.

Either a large oil deposit, or severe wear from insufficient oil in cold conditions can hold the injector partially or completely shut and cause a hard start or no start. A hard start and temporary rough idle when cold is caused by some of the injectors being marginally functional at the start, and the other injectors becoming functional as they warm up from engine heat and soften the oil deposit enough to release the stuck pintle.

A mixture of the two types of CNG fill station compressor oils (mineral and synthetic) is more likely to form injector deposits than either type alone. Vehicles that fill from many stations are more likely to exhibit the conditions. The oil type may also change if a station compressor is serviced or replaced. It is suspected that liquid oil can collect in fill station and vehicle storage tanks and slowly evaporate into the gaseous fuel over several months’ time. Therefore, oil of one type that has collected in a tank can still remain available to mix even after the compressor oil has been changed.

SERVICE PROCEDURE

Different actions are required according to the cause and severity of the conditions exhibited. The actions to correct an insufficient oil situation are different than the actions to correct an excessive oil situation.

Customers reporting the conditions listed above may determine their situation by some quick checks on the vehicle.

EVIDENCE OF INSUFFICIENT OIL INCLUDES:

No oil film on fill station nozzle outlet or vehicle fill receptacle.

No liquid oil found in the bottom of the high-pressure coalescing filter bowl.

A dry coalescing filter element.

EVIDENCE OF EXCESSIVE OIL INCLUDES:

Heavy oil film on station nozzle outlet and vehicle fill receptacle.

Liquid oil in the high-pressure coalescing filter bowl over the level of the white spacer under the element.

Fully oil-soaked coalescing element.

Liquid oil found in fuel tanks or lines opened for other service.

Fill stations that derive compressed natural gas from liquefied natural gas should have an oil injection system. The extremely cold temperature of liquefied natural gas literally ‘freezes out’ lubricants and these lubricants need to be replaced after the gas returns to its vapor phase.

Customers operating their own fill stations (usually fleet customers) should routinely check that all installed equipment is operating properly and is serviced at the intervals recommended by the component supplier. This includes gas dryers, compressors, oil and odorant injectors, particulate filters, and coalescing filters. A fill station may have many filters at different points in the flow stream, such as at the compressor inlet and outlet, dryer inlet and outlet, the storage tank outlet, and the dispenser. A particulate filter that becomes clogged will indicate its condition by high differential pressures or reduced total flow. A coalescing filter that is not drained often enough can fill up with liquids (oil and/or water) and then act as a source of oil contamination for downstream components with no obvious indication at the filter. A fill station technician draining a pressurized coalescing filter too rapidly can rupture the internal element with no obvious indication of trouble, again allowing oil to pass downstream. A compressor that needs to be rebuilt can use more oil than normal due to poor sealing at the piston rings. A fill station maintenance routine should include recording the oil volume drained from downstream filters. This record can be used to compare the oil volume added to the compressor. This will reveal compressor wear and the associated maintenance requirements due to this wear.

Customers who maintain their own vehicles should consider measuring and recording the oil level found in the coalescent filter bowl during routine maintenance. An increase in the oil level found in several vehicles in a short period of time may indicate that a fueling station used by those vehicles requires service to reduce its compressor oil carryover.

Fleet customers should inquire about the maintenance practices of the fill stations they use.

For vehicles known to have excessive oil in their fuel, Ford recommends using the Severe Duty Maintenance Interval of 15,000 miles (25,000 kilometers) to inspect and drain the coalescent filter bowl. Vehicles maintained at this interval and still found to repeatedly have one inch or more of oil in the coalescent filter bowl may require a more frequent maintenance interval. The amount of oil in the fuel does not affect the filter element life, so the element should be replaced at the normal 30,000 miles (50,000 kilometers) interval even if the fuel is known to have excessive oil.

It may also be necessary to clean the CNG fuel injectors using Motorcraft PM- 5 Power Flush Injector Fluid. Refer to TSB #03-18-03 for this service procedure. This cleaning will allow the fuel injectors to return to their normal function. In some fuel environments it may be necessary to perform this cleaning on a regular basis.

NOTE:

IT MAY ALSO BE NECESSARY TO CLEAN OR REPLACE THE FUEL INJECTORS IF THE APPROPRIATE MAINTENANCE INTERVAL IS NOT ADHERED TO. REFER TO TSB #03-18-03 FOR THE INJECTOR CLEANING SERVICE PROCEDURE.